The modern companies usually construct and manage a database storing customer information and personnel information in order to provide services to customers or manage inside operations. The resident registration numbers, addresses, telephone numbers, etc. of the customers and personnel are stored in such the database. According to advancement of hacking skills, leakage of such the important information may become a critical social problem. In order to resolve the above problem, the act on the protection of personal information was legislated, and the government requests companies to prepare measures for preventing the leakage of personal information owned by the companies according to the act. Accordingly, each company manages customer or personnel information in a database by encrypting them. In this case, target data to be encrypted are selected according to the act (i.e. the act on the protection of personal information).
Meanwhile, the database stores actual data such as resident registration numbers, addresses, telephone numbers, etc. together with indexes and constraint conditions (e.g. primary key (PK) and foreign key (FK)). In such the situation, a manager of the database selects target tables and target fields in the target tables for the encryption based on the act. Then, encryption on the target tables and the target fields is performed. However, in such the encryption procedure, conventional encryption techniques may make a problem that the encrypted tables collide with other relevant tables or a problem that relations between the encrypted tables and other relevant tables are destructed. Also, even after the encryption, inside information may be searched by using the indexes, or systems may be changed by using the indexes, whereby critical security risks can be caused.
A method for encrypting a data column, in which indexes of an encryption target column are deleted, the target column is encrypted, and indexes of the encrypted column are regenerated, was disclosed in Korean patent publication No. 2006-0087103. According to such the method for data column encryption, security can be strengthened when a data column for which indexes or PKs are configured is encrypted. However, since indexes of the target column are deleted before encryption, any error occurring during the encryption procedure may damage the original target column or cause data loss in the original target column. Also, since the encryption is performed with data properties of the table being maintained, data length changes according to applied encryption techniques cannot be coped with properly.